Frictional Pressure Loss During Turbulent Flow in Coiled Tubing

Abstract

Abstract Full scale flow experiments were conducted using coiled tubing without a weld bead having 1.75", 2.00", and 2.375" outer diameters on a 98" diameter reel. Experimental results for water agree well with values calculated using previously published formulas. A formula derived by the authors for non-Newtonian fluids gives pressure losses that are in excellent agreement with experimental data for the six fluids considered. Introduction Coiled tubing has several applications in the petroleum industry including drilling, cementing, cleaning sand from a wellbore, acidizing (increasing the permeability at the wellbore wall), scale removal, jet cutting, and formation fracturing. All of these involve pumping fluids through several thousand feet of tubing that has been run into a wellbore from a reel at the surface. The outer diameter (OD) of commonly used coiled tubing and core diameters of reels range from 1.0" to 2.375" and from 72" to 112", respectively. The reel, 98" core diameter, used in our flow tests has a maximum capacity of 14,300 feet of 2.00" OD tubing. The small increase in frictional pressure loss per foot due to the tubing being coiled on a reel may be inconsequential for tubing a few hundred feet long. However, it can be exceptionally important for tubing several thousand feet long. Frictional pressure loss limits the maximum flow rate for any application. Frictional pressure losses of power-law fluids flowing in straight tubing have been extensively studied and accurately modeled for both laminar and turbulent flows. The same is not true for such fluids flowing in coils. The authors know of no published results on the turbulent flow of non-Newtonian fluids in coiled tubing.